问题
I'm considering using pt-online-schema-change to ALTER a primary key (changing it from one column, to a composite primary index) of a table. Are there any limitations to doing this? The documentation states
In most cases the tool will refuse to operate unless a PRIMARY KEY or UNIQUE INDEX is present in the table. See --alter for details.
回答1:
Well, don't do that. Running pt-online-schema-change on a table w/o a single column unique index, may result in a loss of data. See #3 here: http://www.pythian.com/blog/important-caveats-when-using-pt-online-schema-change/
来源：https://stackoverflow.com/questions/28332632/can-i-use-pt-online-schema-change-to-change-a-primary-key